This is an application for a competitive renewal of our grant R01 HL095780-01. We were originally funded to investigate mechanisms underlying the role of the known central desmosomal component, desmoplakin, in the clinical and cellular features associated with the genetic-based heart disease, arrhythmogenic right ventricular cardiomyopathy (ARVC) that causes sudden death in the young, by generating and characterizing novel desmoplakin deficient model systems. For this application, we uncovered synaptosomal associated protein 29 (SNAP29) as a novel desmoplakin associated protein in the adult human heart in a yeast-two hybrid screen that we show has relevance to ARVC, by leveraging our novel genetic mouse and human cardiac models of ARVC. Although the role of SNAP29 is unknown in the heart, we show that SNAP29 co-localizes to cardiac muscle desmosomal cell-cell junctions in the adult mouse and human heart as well as human induced pluripotent stem cell derived cardiac cells (hiPSC). Furthermore, SNAP29 localization and/or levels at desmosomal junctions are lost in hearts from our mouse model of ARVC and ARVC hiPSC-derived cardiac cells that exhibit striking desmosomal defects and arrhythmogenic behavior. Generation of novel SNAP29 deficient mouse models (global and cardiomyocyte-specific) revealed striking cardiac defects including (i) autophagic defects at the cardiac muscle cell junction (accumulation of autophagic/lysosomal markers and structures at the cell junction) that specifically impacted desmosomal protein levels and (ii) cardiac morphology defects. Data from our mouse model of ARVC provides validation to this mechanism as we reveal that their hearts exhibit similar defects in autophagic control at the cardiac muscle cell junction. We hypothesize that SNAP29 regulates desmosomal protein levels and function in cardiac muscle by controlling desmosomal turnover via autophagy-mediated mechanisms and its loss will trigger loss of desmosomal protein levels as well as function and ultimately cause ARVC. We aim to determine: (i) the functional role of SNAP29 in the heart by characterizing SNAP29 loss of function mouse models, (ii) the relevance of SNAP29-DSP interaction in human ARVC and cardiomyocytes by expressing human ARVC mutations and using hiPSCs as a tool, and (iii) the SNAP29-dependent events in autophagy that control desmosomal levels/turnover, by analyzing defects in cardiac autophagy (induction and flux) and relevant desmosome targets using SNAP29 loss of function models and overexpression of SNAP29 in an in vitro ARVC model.